Conventionally, for example, JP 2010-242518 A has disclosed an art relating to a waste heat recovery device that recovers waste heat of an engine. The waste heat recovery device works as a Rankine cycle system having a heat medium that recovers waste heat of an engine main body as a working fluid, and is configured by a water jacket in which a heat medium passing through an inside recovers waste heat and comes into a vapor state, a turbine that recovers power from the heat medium in a vapor state, and a transmission that transmits the power obtained in the turbine to a crankshaft to be capable of varying speed. The power which is recovered by the turbine is used as auxiliary power for the engine.